An arrangement in which a heat exchanger of an evaporator, which heats water to make vapor using exhaust gas heat, is disposed in a combined section of an exhaust manifold of a multicylinder internal combustion engine is known from Japanese Patent Application Laid-open No. 5-340241. Furthermore, an arrangement in which a heat exchanger of an evaporator is disposed in each of the cylinders of a multicylinder internal combustion engine is known from Japanese Patent Application Laid-open No. 56-156407.
However, in the arrangement described in Japanese Patent Application Laid-open No. 5-340241, since the exhaust gas coming out of an exhaust port passes through the exhaust manifold and flows into the heat exchanger, the temperature of the exhaust gas decreases while passing through the exhaust manifold, and there is therefore the problem that the heat exchange efficiency of the heat exchanger deteriorates.
Furthermore, in the arrangement described in Japanese Patent Application Laid-open No. 56-156407, not only are as many evaporators required as there are cylinders, but also pulsations in the exhaust gas immediately after coming out of the exhaust port act on the heat exchanger, and there is therefore the problem that the heat exchange efficiency of the heat exchanger deteriorates at the moment at which the flow of the exhaust gas pulses and stops.